A rolling cone earth boring bit has a bit body with typically three legs. A bearing pin depends from each leg. A cone mounts rotatably to the bearing pin. The cone has a plurality of rows of cutting elements. In one type, the cutting elements comprise teeth machined into the surface of the cone. In another type, the cutting elements comprise carbide compacts or inserts that are pressed-fitted into mating holes in the cone surface.
Each compact has a cylindrical base inserted into a hole and a protruding cutting tip. The cutting tips may have chisel, hemispherical, ovoid or other shapes. Particularly on the heel row, which is located near the gage surface of each cone, the compacts may have asymmetrical shoulder surfaces for engaging the sidewall of the bore hole. Depending upon the formation being drilled, different shapes are utilized for aggressiveness of cutting and durability.
Carbide compacts are very hard, but brittle, thus subject to fracturing. Improvements in reducing stress while maintaining the desired aggressiveness particularly in the inner rows are desirable.